Ferromagnetic material and magnetic apparatus employing the ferromagnetic material

ABSTRACT

A ferromagnetic material can be formed in a very small size on the order of an atomic size and is capable of being stably magnetized. The ferromagnetic material comprises basic unit structures each consisting of a first atom ( 11 ), a second atom ( 12 ) of the same kind as the first atom ( 11 ), and a third atom (or atomic group) ( 13 ) of the same kind as the first atom ( 11 ) or of a kind different from that of the first atom ( 11 ). In each of the basic unit structures, the atoms are arranged on a surface of a substrate so that a chemical bond ( 14 ) is formed between the first atom or molecule and the third atom or molecule, a chemical bond ( 14 ) is formed between the second atom or molecule and the third atom or molecule, and a chemical bond or an electron path ( 15 ) not passing the third atom is formed between the first and the second atom or molecule, wherein said third atoms or molecules consist of As atoms.

CROSS-REFERENCE TO RELEVANT APPLICATION

[0001] This application is a Continuation application of Ser. No.09/375,439, filed Aug. 17, 1999, which is a continuation-in-partapplication of U.S. patent application Ser. No. 08/993,196, filed onDec. 18, 1997, the contents of which are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a ferromagnetic material havinga wide range of application in technical fields, and magneticapparatuses including high-density magnetic recording apparatuses andmagnetic sensors employing such a ferromagnetic material.

[0003] A ferromagnetic material is a substance having spontaneousmagnetization, i.e., a substance having a finite magnetizationintensity. Sometimes, a ferromagnetic material in bulk does not displayany finite magnetization intensity. In such a state, the interior of theferromagnetic material is divided into a plurality of regions, each ofthe regions displays magnetization of a finite intensity, and thedirections of magnetization of the regions are different from eachother. A small region in which spontaneous magnetization has a fixeddirection is called a magnetic domain.

[0004] A ferromagnetic material is applied widely to various magneticdevices including various magnetic recording systems and magneticsensors. Efforts have been made for the development of variousferromagnetic materials suitable for different purposes. In the field ofmagnetic recording, in particular, the reduction in size of magneticdomains and the realization of recording of a minimum unit by a smallestpossible number of magnetic domains are important problems. Although aplurality of magnetic domains serve as a recording unit in currentmagnetic recording, it is desirable to use a single magnetic domain as arecording unit when all is said and done, and it is desirable to reducethe size of magnetic domains each for a recording unit.

[0005] A method of making a ferromagnetic material having small magneticdomains employing electron beam lithography is disclosed in, forexample, Journal of Applied Physics, Vol. 76, pp. 6673-6675 (1994). Thismethod forms a region of several tens nanometer square of magnetic atomson a nonmagnetic substrate, i.e., a material not displayingferromagnetism. It is reported in this paper that the region displaysferromagnetism in a single magnetic domain in some cases. Magnetic atomsare atoms which display ferromagnetism in single bulk, such as those of3d transition metals including Cr, Mn, Fe, Co and Ni, and lanthanidesincluding Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm.

[0006] A region of a ferromagnetic material of a size on the order ofthe foregoing size can be formed by depositing the ferromagneticmaterial on a nonmagnetic substrate with the probe of a scanningtunneling microscope (STM) as mentioned in, for example, Journal ofApplied Physics, Vol. 76, pp. 6656-6660 (1994).

SUMMARY OF THE INVENTION

[0007] Further miniaturization can not be successfully achieved simplyby reducing the size of the region of a magnetic material by the directapplication of the foregoing two methods. Reason for it will beexplained in terms of the Stoner's model which is used for explainingordinary bulky ferromagnetic materials, such as Fe, Co and Ni. Asmentioned in Tokyo Daigaku Bussei Kenkyu-jo, “Bussei Kagaku Jiten”, pp.198-200, Tokyo Shoseki (1996), the Stoner's model expresses a conditionfor displaying ferromagnetism (Stoner condition) by U×D(Ef)>1, where Uis electron correlation energy or energy of Coulomb repulsion betweenelectrons, and D(Ef) is electronic density of states at Fermi level. Asubstance must have a very large density of states D(Ef) on a Fermisurface to be ferromagnetic. However, if a minute atomic cluster systemor a fine atom wire system is formed by a ferromagnetic material meetingthe Stoner condition, the density of states D(Ef) is reduced greatly bya finite size effect and, consequently, the Stoner condition cannot bemet and it is highly possible that the spontaneous magnetization of thesystem disappears.

[0008] Accordingly, a novel idea entirely different from conventionalideas is necessary to realize a ferromagnetic material which makespossible a further smaller single magnetic domain.

[0009] Accordingly, it is an object of the present invention to providea ferromagnetic material from which spontaneous magnetization does notdisappear even if the magnetic domain is further miniaturized.

[0010] A second object of the present invention is to provide a magnetichead capable of controlling a magnetic field created by a minutemagnetic head comprising an atomic group or a fine atom wire formed on asurface of a solid by applying voltage to the surface of the solid ascontrasted with a recording system which supplies a current to anelectromagnetic induction magnetic head.

[0011] A third object of the present invention is to provide amagnetoresistance effect element including a fine wire having a functionsimilar to that of a magnetoresistance device in a spin valve or amagnetic multilayer film (or an artificial super lattice ofmagnetic/nonmagnetic metals) or a function analogous to themagnetoresistance effect of ferromagnetic tunnel junction.

[0012] To solve the foregoing problems, the present invention utilizes afact that the atomic arrangement and the electronic state of a surfaceof a solid, and an atom or an atomic group (including molecules) on asurface of a solid, are different from those of a bulk, i.e., amacroscopic object. Ferromagnetism is displayed by properly arrangingatoms on a surface of a substrate. It is a feature of the presentinvention that ferromagnetism is displayed by using only nonmagneticatoms. Nonmagnetic atoms are those excluding the previously definedmagnetic atoms and atoms of rare gases (He, Ne, Ar, Kr, Xe and Rn).

[0013] As mentioned above, according to the Stoner's model, thecondition for displaying ferromagnetism, i.e., the Stoner condition, isexpressed by U×D(Ef)>1, where U is electron correlation energy or energyof Coulomb repulsion between electrons, and D(Ef) is electronic densityof states at Fermi level. Therefore, even substances which arenonmagnetic in a bulk state can be made to display ferromagnetism if theStoner condition: U×D(Ef)>1 can be met by properly arranging atoms on asurface of a substrate. For example, the appearance of spontaneousmagnetization at an end of a graphite ribbon is theoretically predictedin, for example, Journal of Physical Society of Japan, Vol. 65, pp.1920-1923 (1996). However, this structure has not been realized as yet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1A is a typical view of a basic unit structure of aferromagnetic material;

[0015]FIGS. 1B and 1C are typical views of ferromagnetic structuresformed by cascading a plurality of basic unit structures like that shownin FIG. 1A;

[0016]FIG. 2 is a typical view of the electronic density of statescorresponding to the basic unit of a ferromagnetic material shown inFIG. 1A;

[0017]FIG. 3A is a typical plan view of an atomic arrangement in aferromagnetic material in a first embodiment according to the presentinvention;

[0018]FIG. 3B is a typical side view of a portion of the atomicarrangement near a surface taken in the direction of the arrows A inFIG. 3A;

[0019]FIG. 3C is a typical sectional view of a portion of the atomicarrangement near a surface taken on line B-B in FIG. 3A;

[0020]FIG. 4 is a diagrammatic view of an energy band structure in theatomic arrangement of FIG. 3A;

[0021]FIG. 5A is a typical plan view of an atomic arrangement in aferromagnetic material in a second embodiment according to the presentinvention;

[0022]FIG. 5B is a typical sectional view of a portion of the atomicarrangement near a surface taken on line A-A in FIG. 5A;

[0023]FIG. 6A is a typical plan view of an atomic arrangement in aferromagnetic material embodying the present invention;

[0024]FIG. 6B is a typical sectional view of a portion of the atomicarrangement near a surface taken on line A-A in FIG. 6A;

[0025]FIG. 7A is a typical plan view of an atomic arrangement in aferromagnetic material embodying the present invention;

[0026]FIG. 7B is a typical sectional view of a portion of the atomicarrangement near a surface taken on line A-A in FIG. 7A;

[0027]FIG. 8A is a typical plan view of an atomic arrangement in aferromagnetic material in a third embodiment according to the presentinvention;

[0028]FIG. 8B is a typical sectional view of a portion of the atomicarrangement near a surface taken on line A-A in FIG. 8A;

[0029]FIG. 9A is a typical plan view of an atomic arrangement in aferromagnetic material in a fourth embodiment according to the presentinvention;

[0030]FIG. 9B is a typical side view of a portion of the atomicarrangement near a surface taken in the direction of the arrows A inFIG. 9A;

[0031]FIG. 9C is a typical sectional view of a portion of the atomicarrangement near a surface taken on line B-B in FIG. 9A;

[0032]FIG. 10 is a typical plan view of an atomic arrangement in amagnetoresistance effect element embodying the present inventionconstructed by alternately arranging the ferromagnetic structure shownin FIG. 3A and the nonmagnetic structure shown in FIG. 9A;

[0033]FIG. 11 is a typical plan view of an arrangement of amagnetoresistance effect element in a modification of themagnetoresistance effect element shown in FIG. 10;

[0034]FIG. 12 is a perspective view of a magnetic recording head for onestorage unit, in a preferred embodiment according to the presentinvention, employing the structure of the ferromagnetic material shownin FIG. 3A;

[0035]FIG. 13 is a perspective view of a magnetic recording head for onestorage element, in another preferred embodiment according to thepresent invention, employing the structure of the ferromagnetic materialshown in FIG. 3A;

[0036]FIG. 14 is a diagram showing the variation of expected magneticcharacteristics of the magnetic recording heads of FIGS. 12 and 13 withvoltage applied to the gate electrode;

[0037]FIG. 15 is a typical plan view of an atomic arrangement in amagnetic recording medium embodying the present invention employing thestructure of the ferromagnetic material of FIG. 3A;

[0038]FIG. 16 is a typical plan view of an atomic arrangement in asurface of a magnetic recording head for one byte, which was constructedby employing the magnetic recording head for one storage unit shown inFIG. 13, facing a magnetic recording medium;

[0039]FIG. 17 is a rear view of the magnetic recording head shown inFIG. 16;

[0040]FIG. 18A is a typical plan view of an atomic arrangement in aferromagnetic material in a first embodiment according to the presentinvention;

[0041]FIG. 18B is a typical side view of a portion of the atomicarrangement near a surface taken in the direction of the arrows A inFIG. 18A;

[0042]FIG. 18C is a typical sectional view of a portion of the atomicarrangement near a surface taken on line B-B in FIG. 18A;

[0043]FIG. 19 is a diagrammatic view of an energy band structure in theatomic arrangement of FIG. 18A;

[0044]FIG. 20 is a typical plan view of an arrangement of amagnetoresistance effect element constructed by alternately arrangingthe ferromagnetic structure shown in FIG. 18A and a nonmagneticstructure;

[0045]FIG. 21 is a perspective view of a magnetic recording head for onestorage unit, in a preferred embodiment according to the presentinvention, employing the structure of the ferromagnetic material shownin FIG. 18A;

[0046]FIG. 22 is a perspective view of a magnetic recording head for onestorage unit, in another preferred embodiment according to the presentinvention, employing the structure of the ferromagnetic material shownin FIG. 18A; and

[0047]FIG. 23 is a typical plan view of an atomic arrangement in amagnetic recording medium embodying the present invention employing thestructure of the ferromagnetic material of FIG. 18A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] According to the present invention, a ferromagnetic material isformed by arranging basic unit structures each consisting of nonmagneticatoms or atomic groups arranged on a surface of a nonmagnetic substrate.Nonmagnetic atoms of the same kind or different kinds are arranged on asurface of a nonmagnetic substrate as shown in FIG. 1A by fineprocessing techniques of an atomic level, such as an atomic manipulationtechnique employing a STM. The basic unit structure shown in FIG. 1A hasan atom 11, an atom 12 of the same kind as the atom 11, and an atom 13of the same kind as the atom 11 or of a kind different from that of theatom 11. The atom 13 may be replaced with a molecule, i.e., an atomicgroup. Each atom or each atomic group may be an atom or a moleculeforming the substrate or may be an external atom or an external moleculedisposed on the substrate. The atoms 11 and 12 and the atom (or theatomic group) 13 are arranged so that chemical bonds indicated by solidlines 14 are formed between the atom 11 and the atom (or the atomicgroup) 13 and between the atom 12 and the atom (or the atomic group) 13are chemical bonds, and an electron path indicated by a broken line 15is formed between the atoms 11 and 12. If the basic unit structureincludes an odd number of atoms which do not participate in formingchemical bonds, the basic unit structure has an electronic density ofstates as typically shown in FIG. 2. Although the shape of theelectronic density of states is dependent on the type of the atoms andthe arrangement of the atoms, the density of states has a peak at apoint near the Fermi level. Since the electronic state density has thepeak, the Stoner condition is satisfied and ferromagnetism is displayed.A ferromagnetic material can be constructed by the single base unit orby arranging a plurality of basic unit structures like that shown inFIG. 1A as shown FIG. 1B or 1C. In the following description of variousferromagnetic materials embodying the present invention, atoms of thesame kind are represented by the same mark, and only the representativeone of the atoms of the same kind is indicated at a reference character.Incidentally, a circle with small dots represents the constituent atomsof a substrate, a circle with parallel oblique lines sloping down to theleft represents atoms placed on a surface of the substrate, and a smallsolid circle indicates terminal atoms or hydrogen atoms, i.e., moleculeadsorbates.

[0049] First Embodiment

[0050]FIG. 3A is a typical plan view of an atomic arrangement in aferromagnetic material in a first embodiment according to the presentinvention, FIG. 3B is a typical side view of a portion of the atomicarrangement near a surface taken in the direction of the arrows A inFIG. 3A, and FIG. 3C is a typical sectional view of a portion of theatomic arrangement near a surface taken on line B-B in FIG. 3A.

[0051] In this embodiment, the (100) surface of a Si substrate, i.e., anonmagnetic substrate, is used. All the dangling bonds of Si atoms 31 onthe surface of the Si substrate are terminated by hydrogen atoms 33 toobtain chemically inactive, stable surface structure, the probe of a STMare held close to the hydrogen-terminated surface of the Si substrate,and one row of dangling Si bonds in a fine line was formed by extractingone row of hydrogen atoms by applying appropriate voltage pulses to theprobe. Since the row of dangling Si bonds is chemically more active thanthe hydrogen-terminated Si surface structure, Ga atoms 32 could be madeto be selectively adsorbed by the row of dangling Si bonds by utilizinga thermal evaporation source. A procedure including the foregoing stepsis the same as that mentioned in Japanese Journal Applied PhysicsLetters, Vol. 35, pp. 1085-1088 (1996).

[0052] In this embodiment, the Ga atoms 32 are made to be adsorbedgradually so that the number of the adsorbed Ga atoms is 1.5 times thenumber of the dangling bonds as shown in FIG. 3A. In FIG. 3A, linesbetween the Si atoms 31 and between the Si atoms 31 and the hydrogenatoms 33 indicate chemical bonds. Regions 300 enclosed by broken linesin the surface structure thus formed by arranging the atoms byevaporation correspond to the basic unit shown in FIG. 1A. The Si atoms31, i.e., the constituent atoms of the substrate, correspond to theatoms 11 and 12 of the basic unit structure shown in FIG. 1A. Theseatoms are the constituent atoms of the substrate remaining after theterminal hydrogen atoms 33 have been extracted by the foregoingoperation. The three nonmagnetic Ga atoms 32 correspond to the atom (orthe atomic group) 13 shown in FIG. 1A. In FIG. 3A, the atomic groupconsisting of the three Ga atoms 32 and the constituent atoms 31 of thesubstrate are chemically bonded together. An electron path extendsbetween the atoms 31 via the atomic group of the Ga atoms 32 and anotherelectron path extends between the atoms 31 through the substrate.Therefore, this example has a magnetic domain structure shown in FIG.1B.

[0053] This structure has an energy band structure as shown in FIG. 4,which is known from first-principles calculation based on a localdensity functional method. In FIG. 4, a range between (Γ and Jy showsenergy dispersion relation in a direction parallel to the row of thebasic unit structures. To put it differently, this direction isexpressed by a direction of electrical conduction in the structureconsisting of the basic unit structures; that is, the rows of magneticdomain in this structure are conductive. As is obvious from FIG. 4, theenergy band has a flat section in this direction in the vicinity ofFermi level Ef. Therefore, a peak electronic state density appears at aposition near the Fermi level as typically shown in FIG. 2. Therefore,the structure is expected to display ferromagnetism. Although theresolution of the current scanning magnetic force microscope (MFM) orthe current spin scanning electron microscope (spin SEM) is not fineenough to enable the direct observation of the surface magnetic domainstructure, it is conjectured from the results of scanning tunnelspectroscopic experiments that the regions adsorbing Ga atoms may bemagnetized and the direction of magnetization may be aligned with thefine line of Ga atoms. The results of experiments based on scanningtunnel spectroscopy (STS) proved that the electronic state density has apeak at a position near the Fermi level. The length of the fine line isdependent on the length of a region from which hydrogen atoms areextracted. The shortest fine line corresponds to the basic unitstructure 300 shown in FIG. 3A. It is obvious that long lines can befabricated by the same method.

[0054] Although the constituent atoms 31 of the substrate are Si atomsin this embodiment, a substrate of a semiconductor, such as Ge or GaAs,or an insulating material, such as NaCl, may be used. Although thedangling bonds in the surface of the substrate are terminated byhydrogen atoms 33 in this embodiment, the dangling bonds can beeffectively terminated by atoms other than hydrogen atoms or bymolecules, such as methyl groups. Although the reduction of chemicalactivity by the termination of dangling bonds is very effective infacilitating processing, chemical activity need not necessarily bereduced. Actually, a structure similar to that shown in FIG. 3A can beformed by a processing method which makes the probe of a STM adsorb asmall amount of Ga atoms, holds the probe holding the Ga atoms close tothe surface of a substrate and applies a pulse voltage to the probe totransfer the Ga atoms from the probe to the surface of the substrate. Ifthe substrate is thus processed, the dangling bonds are not terminatedby hydrogen atoms and the arrangement of Ga atoms is somewhat differentfrom that shown in FIG. 3A, but there is not any hindrance to displayingferromagnetism.

[0055] The nonmagnetic atoms 32 may be atoms of a trivalent metal thatbelongs to group III in the periodic table of elements, such as B, Al,In or Tl, or those of a plurality of kinds of metals instead of Gaatoms. For example, a structure similar to that shown in FIG. 3A andcapable of displaying ferromagnetism can be constructed by forming a rowof dangling bonds on a hydrogen-terminated Si substrate, depositing anumber of Ga atoms equal to the number of dangling bonds on the Sisubstrate, and depositing Al atoms equal to half the number of danglingbonds on the Si substrate.

[0056] A ferromagnetic material can be produced by using nonmagneticatoms of a metal of a valence other than those of a trivalent metal. Forexample, a structure formed by depositing a number of Ca atoms, i.e.,bivalent atoms, equal to the number of dangling bonds on a substrate anddepositing a number of Ga atoms equal to half the number of danglingbonds displays ferromagnetism. The arrangement of the atoms on thesurface of the thus processed substrate is not necessarily the same asthat shown in FIG. 3A.

[0057] It is essential that the structure has basic units correspondingto the structure shown in FIG. 1A, and each basic unit structure has anodd number of electrons which does not take part in chemical bonding.More specifically, the arrangement of the atoms may be dependent on thekinds and the numbers of the atoms and the surface structure of thesubstrate.

[0058] It is effective in protecting the ferromagnetic structure tocover the surface of the substrate with an insulating material or asemiconductor so that such ferromagnetic material may not be exposed onthe surface of the substrate after constructing the ferromagneticstructure on the substrate.

[0059] Although the ferromagnetic material in this embodiment isproduced without using any magnetic atoms at all, the ferromagneticmaterial may contain magnetic atoms as an impurity within or in thevicinity of the ferromagnetic structure, provided that the ferromagneticmaterial has basic unit structures corresponding to that shown in FIG.1A and each basic unit structure has an odd number of electrons which donot take part in chemical bonding.

[0060] Second Embodiment

[0061] Referring to FIGS. 5A and 5B, a ferromagnetic material in asecond embodiment according to the present invention is constructed byusing a (111) surface of a hydrogen-terminated Si substrate withoutforming a row of dangling bonds.

[0062] The (111) surface of the hydrogen-terminated Si substrate is keptat a temperature of 80 K, Ga atoms 32 are deposited on the surface ofthe Si substrate, and the Ga atoms 32 are moved with the probe of a STMto form a structure as shown in FIGS. 5A and 5B. In this structure,components corresponding to the atoms 11 and 12 and the atom (or theatomic group) 13 of the structure shown in FIG. 1A are nonmagnetic atoms32, i.e., Ga atoms. The constituent atoms 31 of the substrate need notnecessarily be Si atoms, the nonmagnetic atoms 32 need not necessarilybe Ga atoms, and the terminating atoms (or molecules) 33 need notnecessarily be hydrogen atoms (or molecules). The second embodiment,similarly to the first embodiment, may employ various kinds of atomsother than the foregoing atoms.

[0063] A structure shown in FIGS. 6A and 6B is constructed by arrangingthree structures each being similar to the structure shown in FIGS. 5Aand 5B in three parallel rows. The principle of magnetization of thestructure shown in FIGS. 6A and 6B is the same as that of the structureshown in FIGS. 5A and 5B, and the same structure is able to form amagnetic domain of a large area.

[0064] A structure shown in FIGS. 7A and 7B is similar to that shown inFIGS. 6A and 6B. The structure shown in FIGS. 7A and 7B is constructedby arranging two rows of magnetic domain in parallel to each other withthe adjacent basic unit structures on the two rows of magnetic domainsharing two nonmagnetic atoms 32. The principle of magnetization of thestructure shown in FIGS. 7A and 7B is the same as that of the structureshown in FIGS. 5A and 5B, and the same structure is able to form amagnetic domain of a large area. When arranging a plurality of basicunit structures of the magnetic domain shown in FIG. 1A, the basic unitstructures need not necessarily be arranged on a straight line as shownin FIG. 1B or 1C, but may be arranged in a zigzag arrangement or acircular arrangement resembling a circular arc. The basic unitstructures need not necessarily be arranged in a linear arrangement, butmay be arranged two-dimensionally as shown in FIGS. 5A and 5B, FIGS. 6Aand 6B or FIGS. 7A and 7B. FIGS. 5A, 6A and 7A are plan views of thestructures of the ferromagnetic materials embodying the presentinvention formed by arranging atoms, and FIGS. 5B, 6B and 7B are typicalsectional views of portions of the structures near the surface taken online A-A in FIGS. 5A, 6A and 7A.

[0065] It is effective in protecting the foregoing structure to coverthe surface of the substrate with a protective means, as was mentionedin the first embodiment. The structure, similarly to that of the firstembodiment, is capable of displaying ferromagnetism even if the samecontains magnetic atoms as an impurity.

[0066] Third Embodiment

[0067]FIG. 8A is a plan view of an atomic arrangement in a ferromagneticmaterial in a third embodiment according to the present invention, inwhich basic unit structures of a magnetic domain are arranged in anarrangement corresponding to that shown in FIG. 1C. FIG. 8B is a typicalsectional view of a portion of the atomic arrangement near a surfacetaken on line A-A in FIG. 8A.

[0068] The ferromagnetic material in this embodiment can be produced byextracting hydrogen atoms on a row perpendicular to rows of Si dimers onthe surface of a (100) surface of a hydrogen-terminated Si substrate,bringing a STM probe holding Ga atoms close to the surface of the Sisubstrate, and applying an appropriate pulse voltage to the probe.Measurement by STS showed that the electronic state density in astructure shown in FIG. 8A has a peak at a position near the Fermilevel, and it was inferred from this measurement that the structuredisplays ferromagnetism. In this structure, the constituent atoms 31 ofthe Si substrate, i.e., Si atoms, correspond to the atoms 11 and 12 ofthe structure shown in FIG. 1A, and the nonmagnetic atoms 32, i.e., Gaatoms, correspond to the atoms (or atomic groups) 13 of the structureshown in FIG. 1A. Therefore, it is obvious that the basic unitstructures of the structure shown in FIG. 8A are arranged in the samearrangement as that shown in FIG. 1C. In this embodiment, similarly tothe foregoing embodiments, the constituent atoms 31 of the substrate,the nonmagnetic atoms 32 and the terminating atoms (or molecules) neednot necessarily be limited to Si atoms, Ga atoms and hydrogen atoms(molecules), respectively.

[0069] Fourth Embodiment

[0070] Since the magnetic domain of the basic unit structures shown inFIG. 1A is ferromagnetic and conductive as mentioned above, the rows ofmagnetic domains of the structure shown in FIG. 3A is ferromagnetic andconductive.

[0071]FIG. 9A is a plan view of a structure of a nonmagnetic materialquite analogous with that shown in FIG. 3A but differs from the latterin the arrangement of nonmagnetic atoms 33. This structure does not havea flat portion in a energy band in the vicinity of the Fermi level Ef asshown in FIG. 4, and the electronic state density does not have any peakas typically shown in FIG. 2 at a position near the Fermi level. Thestructure shown in FIG. 9A is conductive and is a nonmagnetic fine line.FIG. 9B is a typical side view of a portion of the atomic arrangementnear a surface taken in the direction of the arrows A in FIG. 9A, andFIG. 9C is a typical sectional view of a portion of the atomicarrangement near a surface taken on line B-B in FIG. 9A.

[0072]FIG. 10 shows a typical plan view of the structure of amagnetoresistance effect element constructed by alternately arrangingferromagnetic regions 43 of fine conductive lines of a structure likethat shown in FIG. 3A and a nonmagnetic region 44 of conductive finelines of a structure like that shown in FIG. 9A. Atoms of the structures43 and 44 shown in FIG. 10 correspond to those of the structure shown in3A and those of the structure shown in FIG. 9A, respectively. In thisembodiment, the length of a nonmagnetic region between the twoferromagnetic regions is 12 Å to couple the two ferromagnetic regionsantiferromagnetically. In this magnetoresistance effect element, theferromagnetic region 43, the nonmagnetic region 44 and the ferromagneticregion 43 are cascaded on the surface of a semiconductor substrate. Anelectric current flows through the magnetoresistance effect element whena voltage is applied across the opposite ends of the magnetoresistanceeffect element, and the intensity of the current varies according to theintensity of an external magnetic field applied to the magnetoresistanceeffect element. Therefore, a magnetism-detecting head employing themagnetoresistance effect element of this embodiment can be used forreading information from a magnetic recording medium.

[0073] A fine line of atoms disclosed in, for example, U.S. Pat. No.5,561,300 or U.S. patent application Ser. No. 08/383,843 may be used forapplying a voltage to the fine line of this embodiment or for sendingout a signal.

[0074] Although this embodiment employs a fine line of the structurecontaining Ga atoms shown in FIGS. 3A and 9A in the ferromagneticregions 43 and the nonmagnetic region 44, any suitable structure ofother atoms or molecules may be used instead of the fine line of thestructure containing Ga atoms, provided that the structure isnonmagnetic and conductive and is capable of antiferromagneticallycoupling the two ferromagnetic regions.

[0075] In the magnetoresistance effect element in this embodiment, theferromagnetic regions 43 are 10 Å in length and the nonmagnetic region44 is 9 Å in length. Therefore, the ferromagnetic regions 43 which issuperparamagnetic at room temperature was ferromagnetic at a lowtemperature of 2.1 K.

[0076] Fifth Embodiment (Embodiment of 3196037843)

[0077]FIG. 11 shows the structure of a magnetoresistance effect elementconstructed by alternately arranging ferromagnetic regions 43 of fineconductive lines of a structure like that shown in FIG. 3A and anonmagnetic region 54 which resembles conductive fine lines of thestructure shown in FIG. 9A. The region 54 of the structure resemblingthat of the nonmagnetic, conductive fine lines shown in FIG. 9A is thesame as the structure shown in FIG. 9A except that the number of Gaatoms included in each basic unit structure of the nonmagnetic region 54of the magnetoresistance effect element of FIG. 11 is less than that ofGa atoms included in each basic unit structure of the nonmagnetic region44 of the magnetoresistance effect element of FIG. 9A by one. Thestructure shown in FIG. 11, similarly to that shown in FIG. 9A, isnonmagnetic, and this fine line is nonconductive. The atoms of thestructure shown in FIG. 11 are the same as those previously describedwith reference to FIGS. 3A and 9A.

[0078] Measurement of the region 54 by scanning tunnel spectroscopy(STS) showed that the nonmagnetic, nonconductive region has an energygap of about 1 eV. The length of the nonmagnetic region is 12 Å tocouple the two ferromagnetic regions on the opposite sides of thenonmagnetic, nonconductive region antiferromagnetically. In thismagnetoresistance effect element, the ferromagnetic region 43, thenonmagnetic, nonconductive region 54 and the ferromagnetic region 43 arecascaded on a surface of a semiconductor substrate, and a tunnel currentflows through the fine line only when a voltage applied to the oppositeends is higher than a critical voltage. The intensity of the tunnelcurrent is dependent on the intensity of an external magnetic fieldapplied to the magnetoresistance effect element. If a magnetic head forreading information from a magnetic recording medium is fabricated byusing the magnetoresistance effect element of this embodiment,information can be read from a magnetic recording medium by applying avoltage that causes a tunnel current to flow to the magnetic head whennecessary.

[0079] Although this embodiment employs a fine line of the structurecontaining Ga atoms in the ferromagnetic regions 43 and the nonmagnetic,nonconductive region 54, any suitable structure of other atoms ormolecules may be used instead of the fine line of the structurecontaining Ga atoms, provided that the structure is nonmagnetic andconductive and is capable of antiferromagnetically connecting the twoferromagnetic regions.

[0080] A fine line of atoms disclosed in, for example, U.S. Pat. No.5,561,300 or U.S. patent application Ser. No. 08/383,843 may be used forapplying a voltage to the fine line of this embodiment or for picking upa signal.

[0081] Sixth Embodiment (Embodiment of 319603742)

[0082]FIGS. 12 and 13 show very small magnetic devices employing theferromagnetic structure shown in FIG. 3A in preferred embodimentsaccording to the present invention. In each of the very small magneticdevices, a fine line 63 of Ga atoms of the structure shown in FIG. 3A isformed on a (100) surface of a Si substrate. The magnetic device shownin FIG. 12 is fabricated by depositing an Au thin film 64 by evaporationon a surface of a Si substrate 60, attaching a Si substrate 62 of athickness on the order of micrometers to the Au thin film 64 so that its(100) surface is exposed, and forming the fine line 63 of aferromagnetic structure as shown in FIG. 3A on the (100) surface. Themagnetic device shown in FIG. 13 is fabricated by forming a fine wire ofa ferromagnetic structure as shown in FIG. 3A on a (100) surface of a Sisubstrate 60, and forming a gate electrode 65 close to fine line of theferromagnetic structure with a small space on the order of micrometersbetween the fine line 63 and the gate electrode 65.

[0083]FIG. 14 shows the voltage-magnetization characteristics of themagnetic devices shown in FIGS. 12 and 13. In FIG. 14, the potential ofthe Au thin film 64 or the gate electrode 65 relative to the fine line63 is measured on the horizontal axis, and value of magnetization ismeasured on the vertical axis. As is obvious from thevoltage-magnetization characteristics, the value M of magnetization ofthe fine line 63 of Ga atoms varies according to the variation of thevoltage Vg applied to the gate electrode 64 or 65 in a fixed range, andthe magnetization of the fine line 63 of Ga atoms can be controlled byproperly determining the gate voltage Vg. The direction of spontaneousmagnetization (spin) is parallel to the fine line 63 of Ga atoms. By amagnetization control method using a gate voltage effect of thisstructure, a minute magnetic recording spot on the order of severalhundreds angstroms can be formed on the surface of a magnetic recordingmedium, by means of a recording operation similar to that of an ordinarybulk magnetic recording head.

[0084] Seventh Embodiment

[0085]FIG. 15 is a typical plan view of an atomic arrangement in amagnetic recording medium embodying the present invention employing thestructure of the ferromagnetic material of FIG. 3A, in which referencecharacters are omitted for simplicity. In FIG. 15, the same marks asthose used in FIG. 3A represent the same atoms, respectively. Atomicfine lines enclosed by broken lines are ferromagnetic. The atomic finelines are magnetized or demagnetized by a magnetic recording head shownin FIG. 12 or 13. Information can be read from the recording medium bydetecting the state of magnetization of the atomic fine lines by amagnetic head provided with the magnetoresistance effect element shownin FIG. 10 or 11.

[0086] Eighth Embodiment

[0087]FIGS. 16 and 17 are a front view and a rear view, respectively, ofa portion of a magnetic recording head for use in combination with arecording medium like that shown in FIG. 15 to be disposed opposite tothe recording medium. In FIGS. 16 and 17, reference numerals 71, 72, . .. , and 78 indicate atomic fine lines of the ferromagnetic structureshown in FIG. 3, and reference numerals 81, 82, . . . , and 88 indicateatomic fine lines forming the magnetoresistance effect element shown inFIG. 10. The atomic fine lines are arranged at intervals equal to thosebetween the longitudinal rows of the magnetic domains of theferromagnetic material of the recording medium shown in FIG. 15 to writeor read one byte of information at a time. As mentioned previously inconnection with FIGS. 12 and 13, the atomic fine lines 71, 72, . . . ,and 78 of the ferromagnetic structure and the atomic fine lines 81, 82,. . . , and 88 forming the magnetoresistance effect elements arearranged in parallel rows spaced a distance on the order of micrometersapart. Terminal pads 91A and 91B are connected to the magnetoresistanceeffect element 81 to connect the magnetoresistance effect element 81 toan external device. Terminal pads 92A and 92B, 93A and 93B . . . , and98A and 98B are connected to the magnetoresistance effect elements 82,83, . . . and 88 to connect the magnetoresistance effect elements 82,83, . . . , and 88 to the external device. A terminal pad 900 isconnected to the atomic fine lines 71, 72, . . . , and 78 of theferromagnetic structure. Wiring lines 811, 812, . . . , 711, 721, . . ., and 710 connecting the atomic fine lines to the terminal pads may bewiring lines extending from the front surface to the back surface byusing the atomic fine lines disclosed in U.S. Pat. No. 5,561,300 or U.S.patent application Ser. No. 08/383,843.

[0088] Information can be recorded on the recording medium by, forexample, the following magnetic recording method. The terminal pad 900is connected to a reference potential, the magnetoresistance effectelements 81 to 88 are set at appropriate potentials corresponding toinformation to be recorded on the recording medium. Consequently, someof the atomic fine lines 71 to 78 of the ferromagnetic structure aremagnetized and the rest are not magnetized as described previously inconnection with FIG. 14, whereby the recording elements of the recordingmedium are magnetized according to information to be recorded, in whichthe recording elements of the recording medium corresponding to themagnetized atomic fine lines are magnetized and those of the samecorresponding to not magnetized atomic fine lines are not magnetized.

[0089] Information recorded on the recording medium can be read by, forexample, the following magnetic information reading operation. Theelectrical resistances of the magnetoresistance effect elements 81 to 88are dependent on the intensity of magnetic field applied thereto.Therefore, currents of intensities corresponding to the magneticallyrecorded information flow through the magnetoresistance effect elements81 to 88 when an appropriate voltage is applied to the terminal padsconnected to the magnetoresistance effect elements 81 to 88 and hencethe information can be read by measuring the currents which flow throughthe magnetoresistance effect elements 81 to 88.

[0090] As is apparent from the foregoing description, according to thepresent invention, ferromagnetic materials and very small magneticdevices can be constructed by using atoms of specific kinds incombination and properly arranging those atoms.

[0091] Ninth Embodiment

[0092] In this embodiment, the As atoms 132 are used instead of Ga atoms32, which are made to be adsorbed on the surface of the Si substrate.

[0093]FIG. 18A is a typical plan view of an atomic arrangement in aferromagnetic material in a ninth embodiment according to the presentinvention, FIG. 18B is a typical side view of a portion of the atomicarrangement near a surface taken in the direction of the arrows A inFIG. 18A, and FIG. 18C is a typical sectional view of a portion of theatomic arrangement near a surface taken on line B-B in FIG. 18A.

[0094] In this embodiment, the (100) surface of a Si substrate, i.e., anonmagnetic substrate, is used. All the dangling bonds of Si atoms 31 onthe surface of the Si substrate are terminated by hydrogen atoms 33 toobtain chemically inactive, stable surface structure, the probe of ascanning tunnel microscope (STM) is held close to thehydrogen-terminated surface of the Si substrate, and one row of danglingSi bonds in a fine line was formed by extracting one row of hydrogenatoms by applying appropriate voltage pulses to the probe. Since the rowof dangling Si bonds is chemically more active than thehydrogen-terminated Si surface structure, As atoms 132 could be made tobe selectively adsorbed by the row of dangling Si bonds by utilizing athermal evaporation source. A procedure including the foregoing steps isthe same as that mentioned in Japanese Journal Applied Physics Letters,Vol. 35, pp. 1085-1088 (1996).

[0095] In this embodiment, the As atoms 132 are made to be adsorbedgradually so that the number of the adsorbed As atoms is 1.5 times thenumber of the dangling bonds as shown in FIG. 18A. In FIG. 18A, linesbetween the Si atoms 31 and between the Si atoms 31 and the hydrogenatoms 33 indicate chemical bonds. Regions 300 enclosed by broken linesin the surface structure thus formed by arranging the atoms byevaporation correspond to the basic unit shown in FIG. 1A. The Si atoms31, i.e., the constituent atoms of the substrate, correspond to theatoms 11 and 12 of the basic unit structure shown in FIG. 1A. Theseatoms are the constituent atoms of the substrate remaining after theterminal hydrogen atoms 33 have been extracted by the foregoingoperation. The three nonmagnetic As atoms 132 correspond to the atom (orthe atomic group) 13 shown in FIG. 1A. In FIG. 18A, the atomic groupconsisting of the three As atoms 132 and the constituent atoms 31 of thesubstrate are chemically bonded together. An electron path extendsbetween the atoms 31 via the atomic group of the As atoms 132 andanother electron path extends between the atoms 31 through thesubstrate. Therefore, this example has a magnetic domain structure shownin FIG. 1B.

[0096] This structure has an energy band structure as shown in FIG. 19,which is known from first-principles calculation based on a localdensity functional method. In FIG. 19, a range between (γ and Jy showsenergy dispersion relation in a direction parallel to the row of thebasic unit structures. To put it differently, this direction isexpressed by a direction of electrical conduction in the structureconsisting of the basic unit structures; that is, the rows of magneticdomain in this structure are conductive. As is obvious from FIG. 19, theenergy band has a flat section in this direction in the vicinity ofFermi level Ef Therefore, a sharp peak of electronic state densityappears at a position near the Fermi level as typically shown in FIG. 2.Therefore, the structure is expected to display ferromagnetism. Althoughthe resolution of the current scanning magnetic force microscope (MFM)or the current spin scanning electron microscope (spin SEM) is not fineenough to enable the direct observation of the surface magnetic domainstructure, it is conjectured from the results of scanning tunnelspectroscopic experiments that the regions adsorbing As atoms may bemagnetized and the direction of magnetization may be aligned with thefine line of As atoms. The results of experiments based on scanningtunnel spectroscopy (STS) proved that the electronic state density has apeak at a position near the Fermi level. The length of the fine line isdependent on the length of a region from which hydrogen atoms areextracted. The shortest fine line corresponds to the basic unitstructure 300 shown in FIG. 18A. It is obvious that long lines can befabricated by the same method.

[0097] Although the constituent atoms 31 of the substrate are Si atomsin this embodiment, a substrate of a semiconductor, such as Ge or GaAs,or an insulating material, such as NaCl, may be used. Although thedangling bonds in the surface of the substrate are terminated byhydrogen atoms 33 in this embodiment, the dangling bonds can beeffectively terminated by atoms other than hydrogen atoms or bymolecules, such as methyl groups. Although the reduction of chemicalactivity by the termination of dangling bonds is very effective infacilitating processing, chemical activity need not necessarily bereduced. Actually, a structure similar to that shown in FIG. 18A can beformed by a processing method which makes the probe of a STM adsorb asmall amount of As atoms, holds the probe holding the As atoms close tothe surface of a substrate and applies a pulse voltage to the probe totransfer the As atoms from the probe to the surface of the substrate. Ifthe substrate is thus processed, the dangling bonds are not terminatedby hydrogen atoms and the arrangement of As atoms is somewhat differentfrom that shown in FIG. 18A, but there is not any hindrance todisplaying ferromagnetism.

[0098] The nonmagnetic atoms 132 may be atoms of a penta-valent metalthat belongs to group V in the periodic table of elements, such as N, P,Sn or Bi, or those of a plurality of kinds of metals instead of Asatoms. For example, a structure similar to that shown in FIG. 18A andcapable of displaying ferromagnetism can be constructed by forming a rowof dangling bonds on a hydrogen-terminated Si substrate, depositing anumber of As atoms equal to the number of dangling bonds on the Sisubstrate, and depositing P atoms equal to half the number of danglingbonds on the Si substrate.

[0099] A ferromagnetic material can be produced by using nonmagneticatoms of a metal of a valence other than those of a penta-valent metal.For example, a structure formed by depositing a number of Ca atoms,i.e., bivalent atoms, equal to the number of dangling bonds on asubstrate and depositing a number of As atoms equal to half the numberof dangling bonds displays ferromagnetism. The arrangement of the atomson the surface of the thus processed substrate is not necessarily thesame as that shown in FIG. 18A.

[0100] It is essential that the structure has basic units correspondingto the structure shown in FIG. 1A, and each basic unit structure has anodd number of electrons which does not take part in chemical bonding.More specifically, the arrangement of the atoms may be dependent on thekinds and the numbers of the atoms and the surface structure of thesubstrate.

[0101] It is effective in protecting the ferromagnetic structure tocover the surface of the substrate with an insulating material or asemiconductor so that such ferromagnetic material may not be exposed onthe surface of the substrate after constructing the ferromagneticstructure on the substrate.

[0102] Although the ferromagnetic material in this embodiment isproduced without using any magnetic atoms at all, the ferromagneticmaterial may contain magnetic atoms as an impurity within or in thevicinity of the ferromagnetic structure, provided that the ferromagneticmaterial has basic unit structures corresponding to that shown in FIG.1A and each basic unit structure has an odd number of electrons which donot take part in chemical bonding.

[0103] A merit of the fine line of the As atoms 132, instead of Ga atoms32, which is made to be adsorbed on the surface of the Si substrate, isthat the electronic density of states near the Fermi level as typicallyshown in FIG. 2 becomes much larger in the case of As atoms 132 than inthe case of Ga atoms 32, since the energy band of the adsorbed As atomsas shown in FIG. 19 is much flatter in the vicinity of the Fermi levelEf than the corresponding energy band of Ga atoms as shown in FIG. 4.This fact strongly favors the occurrence of ferromagnetism, according tothe Stoner's model as was previously mentioned.

[0104] In addition, the specific atomic structure as shown in FIG. 18Ais found to be most stable energetically than other atomic arrangements,as is known from the first-principles calculation based on a localdensity functional method. Therefore, the ferromagnetic material usingAs atoms 132 can be more easily and stably formed, for example, by theabove-mentioned processing method using the STM.

[0105] Tenth Embodiment

[0106]FIG. 20 shows the structure of a magnetoresistance effect elementconstructed by alternately arranging ferromagnetic regions 143 of finelines of a structure like that shown in FIG. 18A and a nonmagneticregion 154. The region 154 of the structure is the same as the structureshown in FIG. 18A except that the number of As atoms included in eachbasic unit structure of the nonmagnetic region 154 is less than that ofAs atoms included in each basic unit structure of the magnetic region143 of FIG. 18A by one. This region 154 does not have a flat portion inan energy band in the vicinity of the Fermi level Ef as shown in FIG.19, and the electronic state density does not have any peak as typicallyshown in FIG. 2 at a position near the Fermi level. Therefore, theregion 154 is nonmagnetic, and this fine line is nonconductive. Theatoms of the structure shown in FIG. 20 are the same as those previouslydescribed with reference to FIG. 18A.

[0107] Measurement of the region 154 by scanning tunnel spectroscopy(STS) showed that the nonmagnetic, nonconductive region has an energygap of about 1 eV. The length of the nonmagnetic region is 12 Å tocouple the two ferromagnetic regions on the opposite sides of thenonmagnetic, nonconductive region antiferromagnetically. In thismagnetoresistance effect element, the ferromagnetic region 143, thenonmagnetic, nonconductive region 154 and the ferromagnetic region 143are cascaded on a surface of a semiconductor substrate, and a tunnelcurrent flows through the fine line only when a voltage applied to theopposite ends is higher than a critical voltage. The intensity of thetunnel current is dependent on the intensity of an external magneticfield applied to the magnetoresistance effect element. If a magnetichead for reading information from a magnetic recording medium isfabricated by using the magnetoresistance effect element of thisembodiment, information can be read from a magnetic recording medium byapplying a voltage that causes a tunnel current to flow to the magnetichead when necessary.

[0108] Although this embodiment employs a fine line of the structurecontaining As atoms in the ferromagnetic regions 143 and thenonmagnetic, nonconductive region 154, any suitable structure of otheratoms or molecules may be used instead of the fine line of the structurecontaining As atoms, provided that the structure is nonmagnetic andconductive and is capable of antiferromagnetically connecting the twoferromagnetic regions.

[0109] A fine line of atoms disclosed in, for example, U.S. Pat. No.5,561,300 or U.S. patent application Ser. No. 08/383,843 may be used forapplying a voltage to the fine line of this embodiment or for picking upa signal.

[0110] Eleventh Embodiment

[0111]FIGS. 21 and 22 show very small magnetic devices employing theferromagnetic structure shown in FIG. 18A in preferred embodimentsaccording to the present invention. In each of the very small magneticdevice, a fine line 163 of As atoms of the structure shown in FIG. 18Ais formed on a (100) surface of a Si substrate. The magnetic deviceshown in FIG. 21 is fabricated by depositing an Au thin film 64 byevaporation on a surface of a Si substrate 60, attaching a Si substrate62 of a thickness on the order of micrometers to the Au thin film 64 sothat its (100) surface is exposed, and forming the fine line 63 of aferromagnetic structure as shown FIG. 18A on the (100) surface. Themagnetic device shown in FIG. 22 is fabricated by forming a fine wire ofa ferromagnetic structure as shown in FIG. 18A on a (100) surface of aSi substrate 60, and forming a gate electrode 65 close to a fine line ofthe ferromagnetic structure with a small space on the order ofmicrometers between the fine line 163 and the gate electrode 65.

[0112] The magnetic devices of FIGS. 21 and 22 displays thevoltage-magnetization characteristics shown in FIG. 14. In FIG. 14, thepotential of the Au thin film 64 or the gate electrode 65 relative tothe fine line 163 is measured on the horizontal axis, and value ofmagnetization is measured on the vertical axis. As is obvious from thevoltage-magnetization characteristics, the value M of magnetization ofthe fine line 163 of As atoms varies according to the variation of thevoltage Vg applied to the gate electrode 64 or 65 in a fixed range, andthe magnetization of the fine line 163 of As atoms can be controlled byproperly determining the gate voltage Vg. The direction of spontaneousmagnetization (spin) is parallel to the fine line 163 of As atoms. By amagnetization control method using a gate voltage effect of thisstructure, a minute magnetic recording spot on the order of severalhundred angstroms can be formed on the surface of a magnetic recordingmedium, by means of a recording operation similar to that of an ordinarybulk magnetic recording head.

[0113] Twelveth Embodiment

[0114]FIG. 24 is a typical plan view of an atomic arrangement in amagnetic recording medium embodying the present invention employing thestructure of the ferromagnetic material of FIG. 18A, in which referencecharacters are omitted for simplicity. In FIG. 24, the same marks asthose used in FIG. 18A represent the same atoms, respectively. Atomicfine lines enclosed by broken lines are ferromagnetic. The atomic finelines are magnetized or demagnetized by a magnetic recording head shownin FIG. 21 or 22. Information can be read from the recording medium bydetecting the state of magnetization of the atomic fine lines by amagnetic head provided with the magnetoresistance effect element shownin FIG. 20.

[0115] While the present invention has been described in detail andpictorially in the accompanying drawings it is not limited to suchdetails since many changes and modifications recognizable to those ofordinary skill in the art may be made to the invention without departingform the spirit and the scope thereof

What is claimed is:
 1. A ferromagnetic material comprising: basic unitstructures each consisting of three nonmagnetic atoms or molecules onsubstrate material of nonmagnetic atoms, wherein, in each of the basicunit structures, the atoms or molecules are positioned so that achemical bond is formed between a first atom or molecule and a thirdatom or molecule, a chemical bond is formed between a second atom ormolecule and the third atom or molecule, a chemical bond or an electronpath not passing the third atom is formed between the first atom ormolecule and the second atom or molecule, and an electronic energy bandhas a flat part at the Fermi level, said ferromagnetic materialexhibiting ferromagnetism, and wherein said atoms or molecules consistof As atoms.
 2. A ferromagnetic material according to claim 1, whereinthe basic unit structures each consist of the three nonmagnetic atoms ormolecules, and the atoms or molecules consist of As atoms.
 3. Aferromagnetic material comprising: a substrate with a row of danglingbonds constructed by extracting H atoms along an Si dimer row from theH-terminated (100) surface of the substrate; and a molecule of three Asatoms arranged on the surface of said substrate, wherein chemical bondsare substantially formed between the molecule and two adjacent danglingbonds only so that an electronic band of an area of the two adjacentdangling bonds and the molecule has a flat part at the Fermi level.
 4. Aferromagnetic material according to claim 1, wherein the substratematerial is selected from the group consisting of Si, Ge, GaAs, andNaCl.
 5. A ferromagnetic material according to claim 3, wherein materialof the substrate is selected from the group consisting of Si, Ge, GaAs,and NaCl.
 6. A ferromagnetic material according to claim 1, wherein eachbasic unit structure has an odd number of electrons which do not takepart in chemical bonding.
 7. A magnetic device comprising: aferromagnetic material comprising basic unit structures each consistingof three nonmagnetic atoms or molecules arranged on a substrate ofnonmagnetic atoms, the atoms being arranged so that a chemical bond isformed between a first atom or molecule and a third atom or molecule, achemical bond is formed between a second atom or molecule and the thirdatom or molecule, and a chemical bond or an electron path not passingthe third atom is formed between the first atom or molecule and thesecond atom or molecule in each of the basic unit structures, and anelectronic energy band having a flat part at the Fermi level; and aconductive material disposed so as to be able to apply an electric fieldto the ferromagnetic material, wherein said atoms or molecules consistof As atoms; and wherein an electron spin state is switched between aparamagnetic state and a ferromagnetic state by a electric field appliedto the ferromagnetic material by the conductive material.
 8. A magneticdevice according to claim 7, wherein the ferromagnetic material isformed on one surface of a semiconductor or insulating substrate, andthe conductive material for applying the electric field to theferromagnetic material is formed on the other surface of thesemiconductor or insulating substrate.
 9. A magnetic device according toclaim 7, wherein the ferromagnetic material and the conductive materialfor applying the electric field to the ferromagnetic material are formedon a same surface of a semiconductor or insulating substrate.
 10. Amagnetoresistance effect element comprising: a substrate of nonmagneticatoms; cascaded regions of a ferromagnetic material comprising basicunit structures each consisting of three nonmagnetic atoms or moleculesarranged on the substrate, the atoms being arranged so that a chemicalbond is formed between a first atom or molecule and a third atom ormolecule, a chemical bond is formed between a second atom or moleculeand the third atom or molecule, and a chemical bond or an electron pathnot passing the third atom is formed between the first atom or moleculeand the second atom or molecule in each of the basic unit structures,and an electronic energy band having a flat part at the Fermi level,wherein said atoms or molecules consist of As atoms; and cascadedregions of a nonmagnetic material comprising basic unit structures eachconsisting of a plurality of atoms arranged so that an electronic energyband does not have any flat part at the Fermi level, wherein theposition of one of those atoms being different from that of the atom ofthe basic unit structure of the ferromagnetic material.
 11. Amagnetoresistance effect element comprising: a substrate of nonmagneticatoms; cascaded regions of a ferromagnetic material comprising basicunit structures each consisting of three nonmagnetic atoms or moleculesarranged on the substrate, the atoms being arranged so that a chemicalbond is formed between a first atom or molecule and a third atom ormolecule, a chemical bond is formed between a second atom or moleculeand the third atom or molecule, and a chemical bond or an electron pathnot passing the third atom is formed between the first atom or moleculeand the second atom or molecule in each of the basic unit structures, anelectronic energy band having a flat part of the Fermi level, whereinsaid atoms or molecules consist of As atoms; and cascaded regions of anonmagnetic material comprising basic unit structures each consisting ofa plurality of atoms arranged so that an electronic energy band does nothave any flat part at the Fermi level and the basic unit structure isnonconductive, wherein the number of the atoms of the basic unitstructure is less than that of the atoms of the basic unit structure ofthe ferromagnetic material by one.
 12. A ferromagnetic materialcomprising plural nonmagnetic atoms on a nonmagnetic substrate, whereinan electronic energy band of said plural nonmagnetic atoms has a flatpart at the Fermi level, and wherein said plural nonmagnetic atoms areselected from penta-valent metals that belong to group V in the periodictable of elements.
 13. A ferromagnetic material comprising pluralnonmagnetic atoms on a nonmagnetic substrate, wherein an electronicenergy band of said plural nonmagnetic atoms has a flat part at theFermi level and wherein said plural nonmagnetic atoms are selected fromthe group consisting of N, P, As, Sn and Bi.
 14. A ferromagneticmaterial according to claim 13, consisting of said plural nonmagneticatoms on said nonmagnetic substrate.
 15. A magnetic device comprising:plural nonmagnetic atoms on a nonmagnetic substrate; and an electrode ata position different from the position of said plural atoms so that saidelectrode is electrically insulated from said plural nonmagnetic atoms,wherein the magnitude of magnetic moment of said plural nonmagneticatoms is changed by applying voltage to said electrode, and said pluralnonmagnetic atoms are selected from the group consisting of N, P, As, Snand Bi.
 16. A magnetic device, having two ferromagnetic domains thatinclude plural nonmagnetic atoms, provided so that a nonmagnetic domainintervenes between said two ferromagnetic domains and said pluralnonmagnetic atoms are selected from the group consisting of N, P, As, Snand Bi.
 17. A magnetic device according to claim 16, wherein each of theferromagnetic domains is made of ferromagnetic material which comprisesplural nonmagnetic atoms on a nonmagnetic substrate, and wherein anelectronic energy band of said plural nonmagnetic atoms has a flat partat the Fermi level.
 18. A magnetic device according to claim 17, whereinsaid ferromagnetic material consists of said plural nonmagnetic atoms onsaid nonmagnetic substrate.
 19. A magnetic device according to claim 18,wherein said plural nonmagnetic atoms are selected from the groupconsisting of N, P, As, Sn and Bi.